You are probably right, but maybe not quite for the reasons you imagine... many of the dams in the northwest run at only a tiny percentage of their possible out

You are probably right, but maybe not quite for the reasons you imagine... many of the dams in the northwest run at only a tiny percentage of their possible output because increasing their productivity could have poor outcomes for fish, etc. So they have already ratcheted back much of their output as a compromise. But - we also have a lot of anti-solar, anti-wind people who try to block those projects for reasons I would call unscientific and emotional. So you can't outright replace the dams just yet either. The dams are also really good at providing a base load, as even when the wind doesn't blow that water just keeps moving.